Radio controlled pilot system



Feb 7, 1950 F. L. MOSELEY RADIO CONTROLLED mm SYSTEM 4 Sheets-Sheet lOriginal Filed Feb. 10, 1941 INVENTOR kc) Female/5L. M06545) Q froimsv.

Feb, 7, 1950 F. L. MOSELEY RADIO CONTROLLED PILOT SYSTEM Original FiledFeb. 10, 1941 4 Sheets-Sheet 2 YQ QQ WIIIIIiIIL N Q L. Mose-15y MAWGMFig.3.

Feb. 7, 1950 F. L. MOSELEY 2 6,80

RADIO CONTROLLED PILOT SYSTEM Original Filed. Feb. 10, 1941 4Shets-Sheet' 3 Fgmc/s L Mos'an W RNEY Feb. 7, 1950 F. 1... M'OSEQLEY2,495,309

RADIO CONTROLLED PILOT SYSTEM Original Filed Feb. 10, 1941 4Sheets-Sheet 4 Patented Feb. 7, 1950 RADIO coN'rnoLtEn PILOT SYSTEMFrancis L. Moseley, Osborn, Ohio, assignor to The Sperry Corporation, acorporation of Delaware Original application FebruarylO, 1941, SerialNo. 378,296. Divided and'this application October 12, 1943, Serial No.505,917 I 24 Claims.

The present invention relates to the automatic control of aircraft, andparticularly to the control of aircraft by signals received fromsuitable remote radio stations located on the ground. The presentapplication is a division of application Serial No. 378,296, filedFebruary 10, 1941, for Radio controlled pilot system, now- Patent 2,-423,336.

one derivative of any. change of heading with re- 7 spect to time.

A still further object of the present invention It has heretofore beenproposed to utilize pcsitional signals transmitted by radio stations foroperating a position indicator located in an aircraft to give a pilot avisual indication of his position. Such signals are produced at thepresent time by means of doubly modulated'transmitters which define aplane of equal modulation. It is also known to utilize a radiotransmitter provided with a suitable antenna setting up a radiationpattern having a constant potential along a line suitable for employmentas a glide'path registering through an indicator to guide a pilot in thelanding of the aircraft. It has further been proposed to employ areceiving loop stabilized in azimuth on the aircraft to define-a'courserelative to a non-directional transmitter.

Any of the above or other radio transmission systems inconjunction-"with suitable receivers,

registering in the aircraft signals varying with the position of theaircraft in space, is suitable for use in connection with the invention.I employ the positional data derived from the radio signals to steer theaircraft automatically, without the agency of the pilot, ona flight pathcoincident which is responsive to the rate of turn of the craft and thespeed of the bank-controlling motor, as modified by a follow-backproportional to the bank of the aircraft.

A still further object of the present invention is to provide novelbridge means for taking derivative voltages for use in controllingaircraft operation.

A further object of the present invention is to provide a novel methodof navigating aircraft, comprising effecting lateral steering responsiveto radio signals indicative of departure from course and rate of changeof departure from course and vertical steering responsive to departurefrom course, rate of change of departure from course, and rate of speedof the elevator control motor. I

A further object of the present invention is to provide a"novelautomatic navigational system wherein hunting of the aircraft about itsline of flight is substantially eliminated through use of novel ratecircuits.

- A still further object of the present invention is to automaticallysteer an aircraft through use with the predetermined radio-definedcourse.

The invention automatically corrects departures of the aircraft from thepredetermined course by suitably correcting the direction of theaircraft for returning the aircraft to the course.

It will therefore be understoodthat the primary object of this inventionis to automatically steer an aircraft on a flight path coincident with apredetermined course defined by positional radio signals.

A further object of the present invention is to provide novel automaticnavigation equipment rate of change of this departure with respect totime, a suitable follow-back means being provided for bringing thesteering control means to null position upon the resumption of thedesired course by the craft.

Another object of the present invention is to ,provide automatic bankingfor aircraft wherein the amount of bank is dependent upon at least ofradio-responsive control means operating automatic pilot means in theaircraft.

- In carrying out these objects I provide a motor forcontrolling thedirection of the aircraft. This motor is controlled by a positionalsignal obtained from a radio receiver which varies in amplitudeaccording to the amount of departure of the aircraft from course.Normally this will be a small DC voltage, and inmysystem this positionalsignal is opposed by a follow-up signal which measures the directionalcorrection through which the aircraft is turned under operation of themotor. When the directional correction is proportional to the departure,the two signals will be equal and opposite and the motor will come torest.

The positional signal obtained from the radio receiver is of the orderof a few microvolts and plified signal is supplied to the other fieldcoil of-y.

the motor. The phase inversion of the amplified signal is dependent uponthe polarity of the origi nal D. C. signal and will operate to controlthen...

direction of the motor.

As used in connection with a doubly modulated transmission system, theradio receiver'out put is constituted by two alternating current sigfnals of different frequencies. These signals are radio transmitters toform radiation fields I and 2 of differing modulation frequencies. Atthe present time modulated frequencies of 90 and 150 cycles areemployed. The two radiation fields define a vertical plane representedas course AB in which the-field strength of the two radiation fields areequal. .By suitable circuits responsive selectively to the differentmodulation frequencies :used in connection with a radio receiver on anaircraft, it is possible to obtain a signal varying with the position ofthe aircraft relative to its departure from course AB.

In order to control the flight path of the aircraft so that it willcoincide with the course AB,

it is necessary to establish in the aircraft a com- Apas's base lineparallel in direction to the course separately rectified and theresulting D. C. po-= 1 tentials bucked against'each other to produce aresultant D. C. signal proportional to the dif ference between theoriginal A. C.xsignals.

Control systems operating as described may be employed for correctinglateral'departures of the aircraft from a course by controlling theheading, and-for correcting vertical departures from course bycontrolling the angle of climb or descent .particularly for landingoperations. According to the invention a complete system will preferablybe provided for controlling the aircraft both horizontally andvertically.

The invention also contemplates automatically controlling the bank ofthe aircraft in dependency on the rate of turn.

In the specific embodiment to be described the :heading and elevationcontrol systems are separately responsive to different radio signals butunder certain conditions Where the aircraft is driven off course bothhorizontally and vertically maysimultaneously operate to return theaircraft to course.

The inventive system will most conveniently be operated in conjunctionwith, and through the agency of, a suitable automatic pilot. Ordinarilysuch automatic pilot will be of the.gyror scopic type and the radioresponsive control motor may perform its function of correcting thedirection of flight through one or more of the direction settingcontrols of the automatic pilot. The operating principles of theinvention, in

regard to the horizontal control of the direction, arebroadly'applicable to dirigible craft, such as surface craft.

craft;

Fig. 3isa circuit diagramof my control device for the turn and bankcontrols of'an aircraft;

Fig. 4 represents the signal and power supply circuits for the operatingunits shown in Fig.3;

Fig. 5 is a circuit diagram of myelevator con trol device.

Fig. 6 represents'the signal su'pplycircuit of the operating unit shownin Fig.5; and,

Fig. 7 is-a diagrammatic representation of the operating relationshipbetween an automatic pilot and the control surfaces of an aircraft.

As shown in Fig. 1, the line AB represents in -a horizontal plane acourse defined by positional radio'signals. This course is produced in aknown manner by the employment of doubly'm'odulated AB, and to controlthe flight path so that its deviation from the established base lineheading varies proportionately to the departure from the course.Assuming an arbitrary departure, the flight .path of an aircraftcontrolled :in this manner is represented by the .path CD, in which thearrows represent the heading of the aircraft as it passes over theflight path. it will be noted that the heading deviation is large underlarge departure, and becomes progressively smaller as the flight pathapproaches the course. The amoii'fit of correction in headingmay be suchas is required under operating conditions, and manifestly theproportionality need not be linear.

It has .been found desirable inorder to avoid hunting of the aircraftabout the course to provide a further control of the air craft headingproportionate to its rate of change of position relative to the course.When this is applied in controlling the heading corrections of the.plane in addition to the correction proportional to th departureitself, the night path of the aircraft under control of my invention isrepresented by apathEF' of Fig. 1. It will be noted that because of thevelocity of the aircraft in its return to .the'course it has been causedto assume a heading parallel to the'course just previous to reaching thesame. This permits the aircraft to attain an exact .oncourse positionthrough its crosswise momentum, so that the aircraft does not overshootthe course. It will be noted that in the flight path CD the aircraftreached its on course position with a slight cross-course velocity whichwould cause the flight path to overshoot the course by a slight amount.Whereas the departure resulting from overshooting the course would beimmediately corrected, the necessity for this is avoided by employing acontrol responsive to the rate of change of the departure.

By utilizing a steering control responsive to the rate of change ofdeparture, it is also possible to obtain anaccelerated correction ofhead- ,ing when the aircraft suddenly departs from course because ofconditions encountered in flight. Because of the relatively largeheading correction in response to a quick departure, the

of direction of the aircraft, and consequently the desired flight "pathmay in general be attained through the described directional correctionsturning the aircraft toward course. The rate of approach to the coursedepends on the angle through which the aircraft is turned toward course,and therefore will likewise vary in proportion to the extent ofdeparture. The control means operating proportionally to the rate ofchange of departure operates to compensate for drift by increasing thedirectional correction of the aircraft in proportion to its velocity ofdrift when such drift opposes its return to course, and decreases thedirectional correction when the drift is toward course, therebymaintaining the desired direction of flight.

It will further be understood that the above principles of operation maybe carried out with any suitable source of positional signal for theaircraft and are in no way dependent on the specific radio systemdescribed. The same principles apply to the control of an aircraft in avertical plane in relation to a suitably arranged source of positionalsignals defining the desired ,course in respect to altitude. As a sourceof such a positional signal it is well known to em ploy either atransmitter setting up a radiation field having the desired coursedefined by a path of constant potential, or to use a doubly modulatedsystem operating to define a positional signal varying with altitude.The directional corrections are applied in the vertical plane to returnthe aircraft to course. The manner in which my invention functions tocarry out the proper steering control procedure to maintain the flightpath in coincidence with the desired course may be described inconnection with Fig. 2. As shown therein, radio range receiver isprovided with antenna 6 for receiving the doubly modulated radiationfield described above. This receiving system is "well known, beingutilized to operate the vertical needle of the cross-pointer instrument1 for the purpose of giving the pilot a visual indication of hisposition relative to the course. The out-' put of the range receiver isutilized to operate the heading control motor 8. This motor controls thedirection of the aircraft in a hori-'- zontal plane through operation ofthe rudder. To obtain the desired actuation of the rudder under controlof motor 8, I contemplate the use of an automatic pilot in the aircraft.In par-' ticular, it is convenient to employ a gyroscopic automaticpilot of the type described in Patent No. 1,992,970 of March 5, 1935,for Hydropneu- 'matic automatic pilot.

This type of automatic pilot is well known in the art, but its operationis diagrammatically illustrated in Fig. 7. The function of the automaticpilot in normal operation is to maintain the orientation of the aircraftconstant in space. This is accomplished under control of suitablegyroscopes described in the above noted patent which actuate throughhydraulically operated motors the control surfaces of the aircraft.Thus, as shown in Fig. 7, rudder 9 is operated by motor Ill under fluidpressur received from oil pressure lines H. In order to obtainproportionate operation of the rudder by the gyroscopic con- ,trolmechanism, a follow-up connection I2 is alsoemployed. Similarly,ailerons I3 are operated by motor 14 with oil pressure lines l5 andfollow-up connection l6. Elevators I! are similarly operated by motor l8provided with oil pressure lines l9 and follow-up connection 20.

;in Patent No. 1,992,970.

The operating mechanism is described in detail 1 The: ,-automatic pilotthus operates to control the orientation ofthe aircraft about the threeprincipal axes simultaneously. Manual control means are normallyprovided for selecting the desired direction .settings. Thus, headingcontrol knob 2| is .provided for the directional gyropilot unit 22 andis operative to vary the heading of the aircraft under the operation ofthe gyroscopic control mechanism. Similarly, bank controlzknob 23 ofgyropilot or bank and pitch gyro 24 is operative to select the desiredangle of bank for the aircraft through operation of the ailerons l3, andelevator control knob 25 is provided to select the desired angle ofclimb or descent of the aircraft. I

As shown in Fig. 2, motor 8 is provided with reduction gearing 26 and isoperatively connected to the heading control 2|, so as to control theheading of the aircraft through the desired op, eration of the rudder.In order to obtain a sufli: cient output to, operate theturn controlmotor 8, I provide turn control amplifier 21 for amplifying the outputof the radio range receiver.

In order toobtain a heading correction proportional to the departure ofthe aircraft, it is necessary to proportion the operation of the turncontrol motor 8 to the amplitude of the positional signal from the,radio rangereceiver. For this purpose it is convenient to employ apotentiom eter 28 in the circuit shown with battery 29, adjustableresistance 30 and center tapped resist.- ance 3|. As shown, thispotentiometer is operatively connected to turn motor 8 and functions tosupply the turn control amplifier with a voltage proportional to theheading correction bucking the positional signal from the radioreceiver. Under control of this circuit turn motor 8 operates to changethe heading of the aircraft only until the follow-up bucking voltage be-.comes vequaland opposite'to' the positional signal, and thereby effectsa heading correction proportional-tothe departure.

Although my turn control mechanism would operate in itself to return theaircraft to the vertical plane of the desired course, better control isobtained byefiecting rigid turns free from skid by banking the aircraftin proportion to the rate of turn. For this purpose bank control motor32 is provided, and is operatively connected through gearing 33 to thebank control 23 of the automatic pilot. In order to obtain bank inproportion to the, rate of turn, I provide a rate of turn measuringdevice comprising an inductanceresistance bridge 34 to be furtherdescribed re-, sponsive to the speed of turn control motor 8. The outputfrom the rate of turn measuring device is amplified in the bank controlamplifier 35 to operate bank control motor 32. In order to obtain bankproportionalto the rate of turn, it is necessary that the operation ofbank control motor 32 be proportional to the rate of turn signal, andfor this purpose I provide a potentiome eter 36 similar in function topotentiometer 28. Potentiometer 36 is operatively connected to bankcontrol motor 32 and supplies a follow-up signal proportional to theangle of bank bucking the rate of turn signal. The amplitude of thefollow-up voltage increases in proportion to the operation of bankcontrol motor 32 and therefore causes motor 32 to bank the planeproportionately to the rate of turn.

In order to prevent overrunning of the bank control motor, andconsequent hunting of the aircraft about the correct angle of bank, rateof bank measuringdevice or resistance-inductance bridge 31 to be furtherdescribed, is provided for measuring the speed of bank control motor 32.The rate of bank signal is introduced into the bank control amplifier toproduce a positive braking action on bank control motor '32 as the inputsignal, determined by the combined rate of turn signal and bank controlfollow-up voltage, approaches zero. Through this means any tendency ofthe bank control motor to overrun the correct setting is automaticallychecked and hunting is avoided.

In order to obtain automatic control of the aircraft in a verticalplane, a glide path receiver 38 with antenna 39 is'util ized. As is wellknown, this receiver supplies a positional signal for operating thehorizontal needle of the cross-pointer instrument I in order to give thepilot a visual indication of his departure from course in altitude. Iemploy this signal "to control the altitude of the aircraft by theoperation of motor 40. Although the altitude control could be obtainedthrough throttle operation, I prefer to use motor 40 to operate theelevator control 25 of the automatic pilot. For this purpose, motor 40is provided with reduction gearing 4i and is operatively connected tothe elevator control 25. Motor 48 is operated from the output of theglide path receiver 38 through elevator control amplifier 39.

In order to obtain a correction proportional to the departure inaltitude, I provide follow-up potentiometer 4'2 operatively connected tomotor II] for supplying a follow-up voltage proportional to the verticaldirectional correction bucking the glide path receiver signal 38.

For the purpose of preventing overrunning of motor 40 and consequenthunting of the aircraft, I provide speed measuring device or bridge 43to be further described to. obtain a signal proportional to the speed ofmotor 40 which is introduced into the elevator control amplifier 39 soas to produce a positive braking action of elevator control motor 40 asthe input signal from the combined glide path receiver signal and thefollow-up voltage approaches zero.

In each case the steering motor is controlled by'a signal measuring thedisplacement from the desired direction, and by a follow-up signalmeasuring the amount of directional correction as the orientation of theaircraft is changed by operation of the motor. When the correction is ofan amount proportional to the deviation to be corrected, the signals areequal and opposite, and no further operation of the steering motoroccurs until a further deviation takes place. Where desirable to preventoverrunning of the motor, its speed is measured, and if it is movingwhen the control signal and follow-up signal are equal, the speed signalpositively brakes the motor to a stop.

In order to measure the rate of departure from course, a circuitcomponent may be employed which is responsive to the rate of change ofthe positional signal and operates to superimpose on the signal acomponent proportional to its rate of change. Such a device isdiagrammatically il- 'Iustrated at 44 for the heading control to befurther described in connection with Fig. 4 and at '45 for the elevatorcontrol to be further described in connection With'Fig. 6. When the rateof change measuring circuit is employed, the directional correctionswill be accelerated and increased in proportion to the rate of change ofdeparture to prevent overshooting on return to course and to minimizedeparture.

It should be mentioned that the operation of the invention has beendescribed in combination with commercially conventional receivers andflight control instruments. These operating units are available for mypurposes in existing aircraft at the present time, and in such instancesmay be economically employed therewith, but it is clear that theoperating principles of my system are independent of the particularunits described, and that other means may be employed.

The operating circuits of my system will now be described.

The control circuits for the turn control motor are shown in Figs. 3 and4. In Fig. 4 is diagrammatically illustrated radio range receiver 5which is responsive to the doubly modulated radiation field illustratedin Fig. 1. The radio range receiver separates the two modulatingfrequencies and provides a dual output. The output signals constitutealternating currents of the respective modulations of the field pattern,and are proportional to their respective amplitudes at the location ofthe aircraft in space. The output signals are amplified by tunedamplifiers 46 and 41 which are coupled to a rectifier network 50 bytransformers 58 and 49. As is well known, the rectifier network producesa direct current signal proportional to the relative strengths of themodulation frequencies of the field pattern, varying in sign independency on which modulating frequency predominates, and falling tozero where the field strengths are equal. In this way a signal isprovided which gives information relative to the position of theaircraft in regard to the radio-defined course.

This signal is used to operate the vertical needle of the cross-pointerinstrument I in a known manner, and in my system is utilized to providethe basic control for the turn motor 8. For this purpose, the signalfrom the rectifier network 50 is led to terminals 5| which areconnectable with the signal input terminals 52 of the turn controlamplifier as shown in Fig. 3. Low pass filter Ifll is provided to removeresidual components of the modulating frequencies which may betransmitted through the rectifier network.

As shown in Fig. 4, I also provide a power supply for the turn controlmotor comprising vibrator 53, transformer 54 and rectifier 55. Thissupplies an alternating current output to terminals 56, and, throughchoke coils 57 and condensers 58, direct current at terminals 59 and 60.

The alternating current supply from terminals 56 is connected toterminals 6| of the turn con trol amplifier, and the direct current fromterminal 60 is connected to terminal 62. The power supply and amplifierare provided with a common ground circuit.

The turn signals from terminals 52 are connected through switch 63 toconductors 64 and 65. Conductor 64 is connected to conductor 66 throughcenter tapped resistance 31 and potentlometer 28, the operation of whichwill be hereinafter described. Conductors 65 and 66 are connected toterminals 61 and 68 of vibrator 69. This vibrator comprises contactpoints Hi and H, and vibrating blade 12 which is actuated by magnet coil13. The output from the vibrator is fed to the center tapped primary 14of transformer 15. The magnet coil of the vibrator is connected to thealternating current source through conductors 16 and I1 and half-waverectifier 18. Consequently vibrator blade 12 is actuated by theresulting current pulses to produce an alternating current intransformer of a frequency equal 9 to the alternating current supply,andofan am 'plitude proportional to the direct current input to thevibrator. The vibrator constitutes in effectamodulator.

Transformer 15 is providedwith secondary 19 which is connected tocontrol grid 89 of'the first turn amplifier tube 8|. Condenser 82'isplaced across the secondary of transformer 15'tcim prove the waveformof the alternating current generated by the vibrator.

The turn control amplifier constitutes a conventional system employing,in additionto the input tube 8|, resistance coupled tubes '83 and 84which feed through tubes 86 and 81. Tubes 86 an'd81 areconnected to thesplit primary 88 of output transformer 89. Primary 88 is shunted bycondenser, toprovide further improvement in the waveform.

'The secondary 9| of transformer'89' couples the amplifier output tofield coil 92 of the turn control motor 8. a j

Turn control motor 8 is also provided with field coil 93 which is fedthrough conductors 94 and 95 by the alternating current supply. 1 Asshown, motor 8 constitutes a two-phase niotor which is operated by thealternating current source and the alternating current generated by thevibrator from the direct current positional signal. It will beunderstood that due to the dependency of the actuating coilof thevibrator on the alternating current supply, the alternating currentgenerated by the vibrator maintains a definite phase relation with thealternating current supply. It will also be understood that thealternating current generated by the vibrator will shift its phaseby,180 .in response to a reversal of direction of the direct currentsignal. The circuit constants of the turn controlamplifier are soadjusted that the output thereof as nearly as possible leads or lags thealternating current by 90. Consequently, motor 8 willoperate independency on the ,direct'current inputto the vibrator, and will respondto a reversal, in polarity thereof by a reversal in its direction ofrotation. l Turn motor 8 is operatively connected to the heading controlof the automatic pilot, as de scribed in connection with Fig. 2. Theoperation of the heading control causes a he'adingvariation of theaircraft which is directlvpropor tional to the movement of the headingcontrol- A Operation of the turn motor 8 actuates potentiometer 28 toset up a voltage between conductors 64 and 66 as the contact armimovesrelative to the midpoint ofthe resistance element. The potentiometer issupplied with the desired voltage gradient by means of battery 29' andrheostat 30. The voltage set up by the potentitransformet 1851push-pullthe output voltage ometer is in direct proportion to the actuation v ofthe heading control, and consequently this voltage is a measure of thedeviation in heading caused by operation of turn motor 8. It willtherefore be understood that operation ofturn motor 8 is inaugurated onthe appearance of a positional signal at terminals 52 indicating'alateral departure of the aircraft from its course, and that the turnmotor continues 'to "operate 'to change the heading for returning theaircraft to course until the voltage set up by potentiometer 28 balancesoutthe positional signal. that is, until the heading correction asnieasure'd by this voltage is equal to the departure'as meas'- "ured bythe positional signalvoltage at terminals 52. In this way the follow-upvoltage from the potentiometer acts to proportionthe head'- ingcorrection of the aircraft to its departure from course, and therebycauses the aircraft to correct its departures by a flight path such asshown at CD in Fig. l. The flight path for correcting departure is undercontrol of the output from potentiometer 28 which is determined by theinput voltage supplied thereto, and by the type of winding, which may belinear or nonlinear as required. It will be understood that the headingcorrection is continuously diminished as the aircraft approaches coursein accordance with the diminishing position signal at terminals 52. I

Manual control of the aircraft may be obtained through my device byoperation of switch 63 to short conductors 64 and 65, whereupon thecon-, trol signal for the turn control motor is obtained from thefollow-up potentiometer 28. The motor therefore runs to restore thesystem '-to balance, with zero input, and in so doing changes theheading of the aircraft.

To employ this action control knob 111 is provided'connected topotentiometer 28 by gearing I16. Operation of knob I11 rotatespotentiometer 28 relative to turn motor 8 by slippage of frictionclutchI15. Motor 8 immediately responds to the output from the potentiometercircuit resulting from movement of the potentiometer from balanceposition, and operates to change the heading until the potentiometer isreturned to balance. a The amount of heading change under manual controlwill be proportional to the rotation given control knob I11, andconsequently the setting of the automatic pilot may be controlledhereby. This is particularly useful when employed inconnection with theautomatic bank control to be described below. j In order to obtain aheading correction proportional to the rate at which the aircraft isapproaching or leaving the course, I may employ circuit means responsiveto the rate of change of the positional signal. As shown in Fig. 4,these may comprise an inductance 9B shunting the re-'- ceiver output,and resistor 91 and condenser 98 which are in parallel to each other andin series with the receiver output. If the direct current signalincreases from a steady state, the re-. actance temporarily assumes ahigh resistance to the increasing current and therefore increases 7proportionately beyond what it would be in the steady state.Simultaneously condenser 98 effectively shunts resistor 91 for therising current and additionally increases the out put to terminals 51.In effect, therefore, the rate responsive circuit superimposes on thereceiver output a signal component proportional to a time derivative, i.e., its rate of change, and thereby increases the heading correction. vI Similarly, in response to movement of the aircraft toward course thereceiver output drops, and inductance 96 generates a shelf-induced current of reverse polarity which further reduces the voltage at terminals5|. At the same time a decreasing voltage is set up over resistance 91and condenser 98 immediately producing a voltage further opposing thereceiver output. In this way, a component proportional to the rate ofdecrease of the positional signal issuperimposed thereupon, and theheading correction of the aircraft is decreased in dependency on therate of approach to course. In the input circuit shown, as the follow-uppotentiometer and the positional signal source are in series, the rateresponsive circuit components 11 also superimpose a component of thecircuit proportional to the rate of change of the potenti- .ometeroutput.

The turn controlmotor operates undert-he basic.

control of a positional signal proportional to departure from course.The basic signalis transformed to an alternating current having thefrequency of a locally generated A. C. supply, is amplified, and isutilized with the locally generated A. C. supply to actuate the turncontrol motor. The change of heading of the aircraft under operation ofthe turn control motor is also measured by a follow-up signal whichopposes the positional signal. In the form shown, the followup signal isconstituted by a D. C. voltage opposing a D. C. positional signal, andthe polarity of the resulting voltage determines whether the amplifiedA. C. signal leads or lags the local generated A. C. supply.

In the embodiment shown wherein the positional signal is derived fromadoubly modulated radiation system it first appears as two alternatingcurrents of diiferent frequencies which are transformed to analternating current of the frequency of the locally generated A. C.supply through rectification to a single direct current signal which isthen converted to A. C. under con trol of the locally generated A. C.supply.

Circuit components have also been shown for superimposing on thepositional signal a component proportional to its rate of change;

It is desirable, in order to avoid side-slip of the aircraft, to bankthe same in proportion to the rate of turn. It will be understood thatunder operation of the automatic pilot heading control the heading ischanged by a constant amount for each revolution of turn motor 8. Inorder to determine the rate of turn of the aircraft, it is thereforeconvenient to measure the speed of turn control motor 8, and to bank theplane in proportion to the speed.

For this purpose I provide an inductance 'esistance bridge comprisingfield coil 92 of the turn motor 8 and resistance I02 as one pair. ofarms, and inductance 99 and resistances I00 and IOI as the other pair.This bridge is balanced by rotating the motor manually to provide aninput voltage for the turn control amplifierv through operation ofpotentiometer 28, and the motor is then blocked in this position. Thetotal value of resistances I00 and [III is then adjusted until the phaseangle of the voltage drop across these resistances is the same as thedrop across resistance I02. The relative values of resistances I00 and IIII are then adjusted without changing their total value so that thevoltage drop across resistance HJI is exactly equal and opposite to thatdeveloped across resistance I02. When the turn motor 8 is allowed torotate, the inductance of field coil 92 will increase to its speed willbe supplied to conductors I 03 and I 04. This speed signal will be of afrequency equal to the alternating current supply, of an amplitudeproportional to the speed of the turn control I receives an alternatingcurrent supply throughv conductors I85 and; IE6. The. potentiometer 36proportionately to the rotation, and an unbalance voltage proportionalis shunted by center tapped. resistor I01. Potentiometer 36' supplies analternating follow-up signal of an. amplitude proportional to thedisplacement of the potentiometer from its center positionand undergoinga phase reversal of 180 as the potentiometer-arm passes from one side to:the other side of the center position. Consequently; the output offollow-up potentiometer 36 may be :caused to .oppose the output from theturn motor speed bridge by suitable phase shifting means inserted in itssupply circuit. For this purpose I provide condenser I08 andinductmice-1:09.

In. order to prevent overrunning of the bank control motor 32,-Iprovidemeans for measuring its speed, which becomes operative to supply aninput control voltage for the bank motor to brake it, should. it.overrun the, primary control signals constituted by .the voltages fromtheturn control motor speed measuring device and the bank motorfollow-up potentiometer. This is constituted .by aspeed responsiveresistance-inductance bridge comprising fieldcoil -I I0 of the bankcon.- trol motor 32, inductance I II, resistance II 2, and resistances II3 and II 4. The outputof this bridge and its operation provide a.signal measuring the speed of the bank control motor similar to .thespeed measuring bridge for turn control motor 8.

The output of the bank motor speed measuring bridge is also proportionalto the rate of change of the output of the bank control motor follow-uppotentiometer circuit, and .to the rate of change of bank caused byoperation of the bank controlmotor.

The bankcontrol amplifier is constituted by resistance coupled tubes 5and H6, which feed push-pull tubes II! and. II 8. Input. transformer H9is provided for the amplifier, and includes secondary I20 feeding thegrid ofthe input tube I I5 and shunted by condenser I2I to improve theA. C. waveform. The push-pull output tubes II! and II 8 feed centertapped primary I22 of output transformer I23 which is shunted bycondenser I 24 also to improve the A. C. waveform.

, Output transformer I23 is provided with secondary I25 for matching theimpedance of field coil II 0 ofthe bank control motor. This motor isalso provided with field I26 excited by the local A. C. supply throughconductors I21 and I28.

The primary I29 of input transformer H9 is included in the bank'motorcontrol circuit which comprisesv theturn control motor speed measuringbridge, the bank control motor follow-up potentiometer, and the bankcontrol motor speed measuring bridge, all connected in series.

The bank control motor operates under a signal comprised of a componentproportional to the speed of the turn control motor, a componentproportional to the bank of the aircraft under operation of the turncontrol motor and bucking the turn motor speed component, and a thirdcomponent proportional to the speed of the bank control motor buckingthe resultant of the. first two components.

Theoperation of the bank control motor speed measuring bridgeis bestconsideredin comparison to the operation of the bank control motorwithout the bridge. In such a circuit the bank control motor wouldrespond to a signal measured by thedifierence' in output between theturn control motor-speed bridge and the bank control motor. follow-uppotentiometer. As the resultant signal varies the bank control motorwould .tendto overrun asbalance is reached, due to its momentum.Ovemnming is; particularly 13 objectionable because it would'result in'hunt-' ing about the proper bank angle as the opera tion of the'bankcontrol motor carries the bank follow-up potentiometer throughthe'balancing position. In order to prevent overrunning of the bankcontrol motor through the position of zero sig nal resulting from thecombined outputs of the wise supplied and reduce its effective value.The

output from the speed measuring bridge may in- --clude a componentproduced b the back E. M. F.

from'the bank control motoron overrunning. As the signal otherwisesupplied approaches zero, the speed responsive component will, in caseof overrunning, assume relatively thereto a large value and may actuallyexceed the other signal to supply a reverse effective signal whichpositively brakes the bank control motor. In any case where the speedcontrol motor is moving to produce a signal from the speed. bridgecircuit, if the signal otherwise supplied is zero, the speed bridgesignal will supply a braking E. M. F. through the bank motor amplifierto the bank control motor which immediately arrests its movement. Inthis way the movement of the bank control motor is immediately arrested.when the turn control motor speed measuring bridge and the bank controlmotor follow-up potentiometer have equal and opposite outputs.

The operating circuits for the elevator con trol motor 40 are shown inFigs. and 6. The operation of this motor is in many respects similar tothat of the turn control motor.

The positional information for controlling the vertical flight pathcomponent is derived from a glide path receiver 38. As is well known,this receiver is utilized in connection with a radio transmitter havinga radiation pattern providing a path of constant intensity along whichthe aircraft is guided. The course defined by the glide path transmitteris utilized to bring the aircraft into a landing. The guide pathtransmitter is modulated at an audio frequency.

.As is usual, the output from the glide path receiver is rectified andoperates the horizontal needle of the cross-pointer instrument I asshown in Fig. 6. The receiver supplies a small D. C. voltage which isgenerally dependent upon the altitude of the aircraft. Low pass filterI82 is provided to remove frequency components which might interferewith the operation of the elevator control motor. the desired course theoutput of the receiver has a definite value, and when the aircraftdeparts vertically from thecourse the receiver out: put increases ordecreases in dependency on the direction of the departure. This outputfrom the glide path receiver is supplied to terminals I3I and I32 asshown in Fig. 6 which are connectable with the input terminals I33 andI34 of the elevator control circuit shown in Fig. 5. In order to obtainapositional signal which re- When the aircraft is on verses its sign independency on which'side of the course the aircraft is, I provideresistance I35 connected to terminal I34. This resistance is in serieswith the output circuit from the glide path receiver and is shunted bybattery I33 and rheostat I31. The current from battery I36 is employedto set up a potential over resistance I35 opposing the output from theglide path re-; ceiver so that the effective input to the elevatorcontrol circuit will be zero when the aircraft is on course, and whichwill change its sign depending upon whether the aircraft is above orbelow the course.

These circuit components in combination with the glide path receiversupply the elevator con:

trol amplifier with a positional signal entirely similar to thatsupplied the bank control amplifier by the rectified input from therange receiver. The elevator control motor 40 similarly operatespotentiometer 42 to supply a follow-up voltage. in combination withbattery I38, rheostat I39, and center tapped resistor I40. The resultantsignal from the combined position signal and follow-up voltage issupplied by conductors MI and I42 to vibrator arm I43 which is operatedby actuator coil I44 energized by the A. 0. supply. from terminals I45.The A. C. supply is rectified to form a series of pulses for operatingthe vibrator I43 by half wave rectifier I46. Thus, the D. C. signal ismodulated at the frequency of the A. C. supply.

The elevator control amplifier receives its ,input through transformerI41 and comprises resistance coupled tubes I48, I49 and I50 and push-,pull output tubes I5I and I52. Its output is coupled to field coil I53of the elevator control motor by transformer I54. The other field coilI55 of the elevator control motor is energized by the A. C. supplythrough conductors I56 and- The operation of this amplifier is in allrespects similar to that of the turn control amplifier, with theexception of the operation of the elevator control motor speed measuringbridge which includes field coil I53 and resistance I58 as one pair ofarms and inductance I59 and resistances I60 and I6I as the other pair.In order to prevent hunting of the aircraft about the course defined bythe glide path transmitter, the output from this speed measuring bridgeis introduced into the elevator control amplifier at control grid I62 oftube I49. The function of this speed responsive signal is in allrespects similar to that.

of the signal produced by the bank motor speed bridge, and it thereforeprevents overrunning of I the elevator control motor 40 and consequenthunting. 1

As described in connection with Fig. 2, the elevator control motor isoperatively connected to the automatic pilot and by operation thereof;controls the angle of climb or descent of the aircraft. The directionalcorrection in the verticalproportional to-therate. 012 chance ofdeparture. in-,a.vertical direction from, course, I employ circuitcomponents for superimposing on. the. positional, signal a componentproportional to its rate of change. These are illustrated in. Fig. 6,and for the purposes ofv illustration. a different circuit has beenshown from that employed with. range receiver 5 for controlling theheading of the aircraft.

The output from the glide pathreceiver is connected by conductors I 64and I65 to a bridge circuit. comprising resistances I66 and IE1. andmutually coupled inductances IE8v and IE9. The output from the bridge,circuit is supplied to terminals I3I and I32 through conductors I'll)and III. It will be understood that in a steady-state conditioninductances I68 and I69. effectively shunt the output. received atterminals I3I and I32, but that they oppose a proportionately in.-creasing resistance on a rising signal to increase the output relativeto their action in a steadystatecondition; and generate an opposingvoltage on a decreasing signal to reduce the output relative to theiraction in a steady-state condition. The bridge therefore superimposes onthe positional signal a component proportionalto its rate of change, andthe resulting signal supplied at terminals I3I and I32 causes theelevator control motor to correct the direction of the plane inproportion to the rate of change of departure-in the vertical relativeto the-course defined bythe glide path transmitter.

It will be understood that in landing the automatic vertical control ofthe aircraft should be immediately terminated on contact of the aircraftwith the ground either'automatically or by a manual control operable bythe pilot. For this purpose switch I'ISis provided in conductor I5] fordeenergizing the field coil I55"of the elevator control motor 40.

In accordance with the above description it will be understood that theinvention contemplates the completely automatic control of the flight ofan aircraft in dependency on positional information derived from radiosignals. Under operation of my system the aircraft is automaticallyguided to maintain the desired course. The system is similarly designedto automatically land an aircraft, which operation is automaticallycarried out without requiring any manual control dependent upon thepersonal judgment of the pilot.

Whereas it is desirable to employ the complete system. under certaincircumstances only certain components thereof need be utilized. Forinstance, my turn control unit either withor without the bank controlunit may be employed in instances where it is unnecessary to maintain anautomatic control of the altitude of: the aircraft. Similarly, thealtitude control unit may be used alone, where automatic control of turnand bankof the aircraft is not desired. It is clear that the operatingprinciples of my system are not restricted in any way to. the specificcircuits described. but maybe utilized in'other embodiments.

What is claimed is:

1. In a control system for dirigible craft, electric motor meanscontrolling the direction of movement of the craft. control circuitmeans for the motor means operative in response to a directionaldisplacement signal to cause operationof the motor means, and furthercontrol means for the motor-means connected for receiving saiddisplacement signal and operative to correct a por tionzof thesametosupply atimezderivativasignal to. said control cirouitmeansto brakethemotor means onoverrunning following decreasing effective value of saiddisplacementsignal.

2. In anaircraft flight control. system, electric motor means operativeto control the heading of the aircraft, control circuitmeans for themotor means for receiving a control signalresponsive to change inposition of the aircraft, follow-up control means for the motor meansresponsive. to the operation of the motor means connected for supplyingafollow-up signal to said control circuit means,.and anti-huntingcontrol. means for the motor meansresponsive. to the rate of operationof the motor means also connected to said control circuit means.

3. In an aircraft. flight control system, in combination, electric motormeans operative to control the direction of flight of the aircraft,signal input circuit means controlling operation of the motor means forreceiving an input control signal voltage, follow-up means operated bythe motor means operative tov supply a voltage to the signal inputcircuit means opposing: the input control signal voltage, and meansresponsive to the speed of the motor means operative to supply a speedvoltage to the signal input circuit for preventing hunting of theaircraft about its desired line of flight.

4'. In an aircraft flight control'system, in combination, electricallyoperated motor means operative to control the direction of flight of theaircraft, control, circuitmeans' for the electrically operated motormeans adapted to receive a control signal for controlling operation ofthe motor means, follow-up means operated by. said motor means forsupplying a signal forcounteracting said control signal, and meansconnected to said motor'means and becoming operative upon the effectivecontrol signal approaching zero to-supply an anti-huntingsignal to thecontrol circuit means proportional tov the speed of the motor means forbraking the motor;

5.. In. an aircraft flight. control system, position-responsive meansfor supplying a positional signal proportional totheextent of departureof the aircraft from av course, motor means operative-to control thedirection of flightof the aircraft operating in dependency onthe-positional signal supplied by position-responsive meansto return.the aircraft to course, follow-up means operated by the motor meansoperative to supply a follow-up signal proportional. to the operation ofthe motor means opposing the positional signal and balancing out saidsignal on operation of the motor means proportional to the positionalsignal, thereby controlling the operation of the motor means, and meansoperating in. dependency on the speed of the motor means supplying a,signal proportional to thespeed of. the motor means opposing thepositionalsignal and operative to brake the motor'means as thepositional and follow-up signals approach balance.

6. In an aircraft flight control system, motor means operative tocontrol the direction-of flight of the aircraft, control means'connectedfor controlling said motor means responsive to a signal proportional tothe'extent of departure and to the rate-ofdeparture of the aircraft froma'course to cause the motor means to return the aircraft to course,follow-up control means connected for further controlling the motormeans responsive tov the operation of. the motor means, and antihuntingmeans connected for further controlling said: motor means.

'7. In an aircraft: flight? control system; motor means: connected so asto be operative to control the direction of flight of the aircraft, acontrol circuit for said motor means responsive to departures of saidaircraft from course and to a time derivative thereof, and follow-up andantihunting control means for the motor means responsive to theoperation and to the rate of operatlon of the motor means and connectedfor controlling said motor means.

8. In an aircraft flight control system, aircraft flight controllingmotor means connected so as to be operative to control the direction offlight of the aircraft, and control means for the motor means responsiveto change of direction and to rate of change of direction of theaircraft under operation of the motor means connected for controllingsaid motor means.

9. In an aircraft flight control system, in com bination, motor meansoperative to control the direction of flight of the aircraft, a signalcircuit, a motor controlling input circuit, a motor-move ment responsivefollow-up circuit, a motor speed responsive circuit, the signal circuitbeing connected with the motor controlling input circuit to causeactuation of the motor responsive to the signal, the motor-movementresponsive circuit being connected to the input circuit to oppose thesignal on actuation of the motor and operative to render the inputcircuit voltage from the signal and motor-movement responsive circuitszero on motor movement proportional to the signal, the motor speedresponsive circuit being operative to supply the input circuit with abraking voltage to stop the motor when the voltage supplied to the inputcircuit by the signal and follow-up circuits is substantially zero andthereby prevent overrunning of the motor.

10. In an automatic navigational system for dirigible craft, electricsteering motor means for controlling the steering of the craft, andcontrol means for said steering motor means responsive to departure ofthe craft from a desired heading and to the first derivative of suchdeparture with respect to time, and follow-back means responsive tooperation of said steering motor means connected to said control meansfor modifying the action of said control means.

11. In an automatic navigational system for dirigible craft, a radiorange receiver for producing an output signal responsive to departure ofthe craft from a desired radio course, means supplied with said signalfor deriving from said out put signal a signal responsive to the rate ofchange thereof, electric motor means for controlling the steering of theaircraft, and a control circuit for said motor connected to beresponsive to said signals.

12. In an automatic navigational system for dlrigible craft, a radiorange receiver for producing an output signal responsive to departure ofthe craft from a desired radio course, means connected to said receiverfor deriving from said outputv signal a signal responsive to the rate ofchange of said signal, electric motor means for controlling the steeringof the aircraft responsive to said signals, means responsive to thespeed of said motor means for producing a rate signal and additionalelectric motor means for controlling the banking of the aircraftconnected to be responsive to the rate signal of said speed responsivemeans.

13. An automatic navigational system for dirigible craft as defined inclaim 12, wherein means is provided responsive to the rate of operationof 18 said banking motor means to substantially eliminate the huntingthereof.

14. In an automatic navigational control system for aircraft, aglidepath radio receiver for producing an output voltage signal responsive todeparture of the craft from a desired glide path, means connected in theoutput circuit of said receiver for taking a derivative of said outputsignal, and an elevator control motor for said aircraft having a controlcircuit connected to be responsive to said signal and its derivative.

15. An automatic navigational control system for aircraft as defined inclaim 14, wherein antihunt means is provided for further controllingsaid elevator control motor responsive to the speed thereof, saidanti-hunt means being con-I nected in said motor control circuit.

16. In a navigational system, steering and aileron control motors,circuit means for producing a voltage varying with the speed of a motorhaving said steering control winding varying in effective impedance withchange of motor speed, comprising a bridge circuit including saidwinding in one arm thereof, means for applying a control voltage to apair of opposite bridge points of said circuit, and output connectionsto other bridge points thereof.

17. A navigational system. as defined in claim 16, wherein means isprovided for connecting said steering control motor for operating theaircraft rudder, and additional means, connected for operating theaircraft aileron control motor, connected to be controlled from saidoutput connections, whereby the operation of said aileron control motoris proportional to the speed of said steering control motor.

13. In apparatus of the character described, a bridge circuit forderiving a derivative potential comprising resistances and mutuallycoupled inductances, said inductances serving to effectively shunt asupply potential connected to opposite bridge points during a steadystate condition of the supply potential, said inductances offering anincreasing resistance to a rising supply potential and generating anopposing voltage upon a decreasing supply potential, thereby superposingon the supply potential a component proportional to its rate of change,the output of said bridge being removable from the remaining oppositepoints thereof.

19. In apparatus for automatically steering a dirigible craft to followa predetermined radio course, a receiver for producing a course signal,direction control means operable to alter the orientation of said craftabout an axis, motive means connected to be responsive to said signaland operably connected to said direction-controlling means, additionaldirection control means operable to alter the orientation of said craftabout an axis at right angles to said first axis, and second motivemeans connected to be responsive to the rate of operation of said firstmotive means operably connected to said additional control means.

20. Circuit means for obtaining a voltage dependent upon the speed of amotor having a winding varying in effective impedance with change ofmotor speed, comprising a bridge circuit including said winding in onearm thereof, means for applying an input to a pair of opposite bridgepoints of said circuit, output connections to conjugate bridge pointsthereof, and means for balancing said circuit at a predetermined motorspeed, including zero speed.

21. Circuit means for obtaining an alternating voltage dependent uponthe speed of a motor having a winding varying in effective impedancewith change of motor speed, comprising an impedance bridge circuitincluding said winding in one arm thereof, means for applying analternating electrical input to a pair of opposite bridge points of saidcircuit, output connections to conjugate bridge points thereof, andmeans for balancing said circuit at the frequency of said input and atzero or a predetermined motor speed.

22. Circuit means for obtaining a reversible phase alternating voltagedependent upon the speed and direction of operation of an alternatingcurrent motor having a winding varying in reactance as to magnitude andsign with variation of motor speed and direction of rotationrespectively, comprising an impedance bridge including said winding inone arm thereof, means for applying an alternating electrical input to apair of opposite bridge points of said circuit, output connections toconjugate bridge points thereof, and means for balancing said circuit atthe frequency of said input and With said motor at standstill.

23. In an aircraft flight control system having a turn control motor forcontrolling the steering rudder of an aircraft, means operative by andwith said turn control motor for producing a signal voltage proportionalto the speed thereof, a

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,896,805 Sperry et a1 Feb. 7,1933 2,102,141 Wager Dec. 14, 1937 2,105,598 Hubbard Jan. 18, 19382,115,086 Riggs Apr. 26, 1938 2,159,142 Fisher May 23, 1939 2,221,612Schaelchlin Nov. 12, 1940 2,237,440 Jones Apr. 8, 1941 2,283,754Matthews May 19, 1942 Certificate of Correction Patent No. 2,496,809February 7, 1950 FRANCIS L. MOSELEY It is hereby certified that errorsappear in the printed specification of the above numbered patentrequiring correction as follows:

Column 10, line 62, for shelf-induced read self-induced; column 18,lines 20 and 21, for of a, motor having said steering control read ofsaid steering control motor having a; and that the said Letters Patentshould be read with these corrections therein that the same may conformto the record of the case in the Patent Office.

Signed and sealed this 23rd day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uommiasioner of Patents.

Certificate of Correction Patent No. 2,496,809 February 7, 1950 FRANCISL. MOSELEY It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 10, line 62, for shelf-induced read self-induced; column 18,lines 20 and 21, for of a motor having said steering control read ofsaid steering control motor having a; and that the said Letters Patentshould be read with these corrections therein that the same may conformto the record of the case in the Patent Oflice.

Signed and sealed this 23rd day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Uonmniasimwr of Patents.

